Heterogeneous CuxO Nano-Skeletons from Waste Electronics for Enhanced Glucose Detection

Highlights Novel laser-induced transfer method for fabricating glucose sensors from recycled e-waste copper, offering a sustainable and cost-effective solution. Unique heterogeneous CuxO nano-skeletons derived from discarded printed circuit boards exhibiting exceptional glucose-sensing performance (sensitivity: 9.893 mA mM−1 cm−2, detection limit: 0.34 μM). Miniaturized glucose detection device, optimized for scalability and portability, revolutionizing diabetes management and patient care. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-024-01467-5.


Supplementary Figures
Fig. S1 The optical and corresponding grayscale images of the PCB Fig. S2 The optical photo of PCB before and after varnish removal Nano-Micro Letters S2/S16 Fig. S3 The procedures and optical image of the fully automatic fabrication system Note: We designed and fabricated this system.The system comprises four main components: a spin robot equipped with four arms positioned at 90-degree intervals for holding glass sheets, a glass sheet injector supplying glass sheets to the robot arm, a carbon cloth conveyor for transporting carbon cloth, and a laser system.Fabricating the working electrode involves four steps in this automated system.First, a robot arm retrieves a glass sheet from the injector (Fig. S3a, Step 1).Then, the arm rotates 90 degrees, positioning the glass sheet over the PCB for the LIBT process, which recycles copper from waste PCB onto the glass sheet (Fig. S3b, Step 2).Next, the arm moves to the carbon cloth conveyor, initiating a LIFT process to transfer copper from the glass sheet to the carbon cloth (Fig. S3c, Step 3).Once completed, the carbon cloth shifts 2 cm to expose raw material for laser treatment in the subsequent LIFT process.Finally, used glass sheets are removed and stored (Fig. S3d, Step 4).With this automated system, electrodes can be continuously produced once laser fabricating parameters are established, and the optical image of the fully automatic fabrication system is shown as Fig. S3e.Copper transferred onto the carbon cloth serves directly as the working electrode for glucose detection.

Note:
To further investigate the oxidation kinetics of the forward-transferred copper particles under different laser frequencies, we developed a simplified model for computing the temperature distributions within the donor layer when irradiated by a single laser pulse.The calculation principle is referenced from the classical laser radiation theory [S1] and our previous report [S2].The donor material experiences a transient increase in temperature to an ultra-high level when absorbing laser energy.The rising temperature ΔT can be calculated based on a function about the radial distance from the donor's surface (r), the depth of the donor layer (z), and processing time (t): The temperature increase as a function donor depth at the center of the laser beam (r = 0) was calculated using Eq. ( S1), which takes into account the pulse intensity (Imax), Fresnel energy reflectivity (R), copper's thermal diffusivity (K), copper's thermal conductivity (γ), laser beam's mode field radius (W), and pulse width (τ).For simplicity, a square-shaped pulse was assumed, determined by the temporal function p(t).
As demonstrated in the curves of calculated rising temperature vs. donor depth (Fig. S8), the laser pulses with frequencies from 100 to 500 kHz contribute to the ultra-high transient temperatures (~8,000 to 40,000 K) in the near-surface of the donor.These calculated theoretical temperatures are far higher than the boiling point of copper.Vaporization and even ionization will occur in the irradiated copper particles.Apparent plasma generation can be observed during the LIFT process.The rapid generation and expansion of copper vapor/plasma will result in the formation of laser-supported detonation waves (LSD), promoting the high-speed transfer of copper-based particles [S3, S4].The laser pulse with a lower laser frequency will lead to a higher surface temperature of the donor, contributing to a more intense micro-detonation and a more rapid transfer process.
Figure S10 shows the transfer time positively correlates with the laser frequency under the irradiation of a single laser pulse

Note: Calculation in LIFT process
The calculation principle is referenced from the classical laser radiation theory and our previous report [S1, S2].The operation software sets the operating powers P0, pulse frequency fL, and pulse width τL.The laser power meter was used to test the laser output power (P).Equations ( 3) and (4) can be used to calculate the light intensity I and pulse energy fluence F, respectively: As shown in Table S2, with the fixed operating power and pulse width, the laser output laser pulses deliver a constant average output power of 6.44 W. Therefore, the pulse energy fluences decrease from 13.12 to 2.62 J cm −2 when the pulse frequencies increase from 100 to 500 kHz.It should be noted that in a near-continuous laser mode (at 100 ns pulse width and ~10000 pulse frequency), the energy fluence corresponding to every single pulse is low (0.13 J cm −2 ).

Fig. S4
Fig. S4 Record image of PCB LIBT process

Fig. S6 a
Fig. S6 a SEM image of PCB Cu LIBT to glass sample.b magnified image from the labeled region in a Note: The SEM image shows that the bulk copper became bridged nanoparticles after the LIBT process.

Fig. S7
Fig. S7 Record image of PCB LIFT process

Fig. S8
Fig. S8 XRD of samples by different frequency (CC represents the pure carbon cloth treated by laser with CW mode) Note: The XRD result shows that the samples gotten under relatively low laser frequency are the mixture of Cu2O and Cu.And the peaks intensity corresponding to Cu decreases with the increasing of frequency until the peak of Cu almost disappears when the laser beam is working in continuous-wave (CW) mode, indicating the sample under CW moder is Cu2O.

Fig. S9
Fig. S9 Calculated rising temperature vs. donor depth at the center of the laser beam (r = 0).

Fig. S10
Fig. S10 The influence of laser frequency to transfer time proportion Note: The proportion of actual laser transfer time (p (%)) under a single laser pulse irradiation is calculated via Eq.(S2):

Fig. S11 Fig. S13 a
Fig. S11 CV of samples by different laser frequency with 0.5 M glucose at 50 mV/s

Fig. S15
Fig. S15 CV curves of the h-CuxO, commercial Cu2O, and CuO electrodes before and after CA activation

Table S1
The mass reduction of the PCB vs. the corresponding mass increase of the glass sheet

Table S2
Measured laser output power, calculated light intensity, and calculated pulse energy fluence vs. set laser operating power and laser frequency

Table S3
Comparison of the glucose detection performance of various electrodes